This invention relates to a partial oxidation reformer for reforming hydrocarbon-based feed gas by partial oxidation reaction to produce hydrogen for the supply to fuel cells or the like.
In general, hydrogen can be produced by reforming hydrocarbon or methanol. Fuel reforming units for producing hydrogen through such reforming can be used for fuel cells, hydrogen engines or the like.
As a reforming unit of such kind, there is conventionally known one which is incorporated into a fuel cell system as disclosed in Japanese Unexamined Patent Publication No. 11-67256. This fuel reforming unit includes a fuel reformer loaded with catalyst which exhibits activity to partial oxidation reaction, and is designed to introduce feed gas into the fuel reformer to produce hydrogen by partial oxidation reaction of the feed gas.
Specifically, in the partial oxidation reaction, feed gas containing methane, oxygen and water is partially oxidized to convert into carbon dioxide and hydrogen as expressed in the following chemical formula and heat of reaction is produced during the reaction.
CH4+(xc2xd)O2+H2Oxe2x86x92CO2+3H2
Meanwhile, as another reforming unit of such kind, there is known one including a reforming reaction section with a structure in which a pipe (housing) is loaded with particulate catalysts or a monolith. In this unit, there arises the problem that heat of reaction in the reforming reaction section, which may be elevated to for example about 800xc2x0 C., is likely to flow outside as heat loss so that temperature variations occur in the reforming reaction section to deteriorate the efficiency of reaction and thermal efficiency. In order to avoid heat of reaction from dissipating outside, it is necessary to provide a thick thermal insulant around the pipe.
Further, in order to promote partial oxidation reaction of feed gas in the reforming reaction section, it is necessary to preheat the feed gas being fed to the reforming reaction section to a predetermined temperature (for example, 460xc2x0 C.) and in order to implement such preheating, it is also necessary to provide a preheater formed of a heat exchanger.
An object of the present invention is therefore to reduce temperature variations in the reforming reaction section, improve the thermal efficiency thereof and provide the reformer with a simple and compact construction, by contriving the construction of the reformer.
To attain the above object, in the present invention, the reformer is of a double-wall structure type and a reforming reaction section and a feed gas passage are disposed inside and outside of the inner wall, respectively.
More specifically, the present invention is directed to a partial oxidation reformer having a reforming reaction section (6) for producing hydrogen-rich reformed gas from feed gas by reaction including partial oxidation. In this reformer, a feed gas passage (3) through which the feed gas is supplied to the reforming reaction section (6) is provided in the vicinity of the reforming reaction section (6).
Thus, the sides of the reforming reaction section (6) are covered with the feed gas passage (3) and therefore thermally insulated by the feed gas passage (3). As a result, temperature variations in the reforming reaction section (6) can be reduced.
Further, conversely, the feed gas in the feed gas passage (3) in the vicinity of the reforming reaction section (6) is heated by heat of reaction in the reforming reaction section (6). Accordingly, the heat of reaction in the reforming reaction section (6) can be recovered for the purpose of preheating the feed gas. Such self-recovery of heat can improve the thermal efficiency of the reformer.
In addition, since the heat of reaction in the reforming reaction section (6) heats the feed gas in the feed gas passage (3) around the reforming reaction section (6) in the above manner, a preheater for preheating the feed gas can be formed integrally between the feed gas passage (3) and the reforming reaction section (6). This makes the construction of the reformer simple and compact.
Alternatively, in a partial oxidation reformer of the present invention which has a reforming reaction section (6) for producing hydrogen-rich reformed gas from feed gas by reaction including partial oxidation, a heat exchanger (14) is provided for exchanging heat between the reformed gas in a reformed gas passage (11) communicating with an outlet (6b) of the reforming reaction section (6) and the feed gas in a feed gas passage (3) communicating with an inlet (6a) of the reforming reaction section (6).
Thus, the feed gas in the feed gas passage (3) which should be supplied to the reforming reaction section (6) is heated in the heat exchanger (14) through the heat exchange with the reformed gas heated to a high temperature by heat of reaction in the reforming reaction section (6). Accordingly, the heat of reaction in the reforming reaction section (6) can be recovered for the purpose of preheating the feed gas and such self-recovery of heat can improve the thermal efficiency of the reformer.
In addition, since the heat of reaction in the reforming reaction section (6) heats the feed gas in the feed gas passage (3) in the above manner, a preheater for preheating the feed gas is formed integrally between the feed gas passage (3) and the reformed gas passage (11). This makes the construction of the reformer simple and compact.
The reforming reaction section (6) and the feed gas passage (3) may be provided integrally in a housing (1). This further simplifies the construction of the reformer, resulting in cost reduction.
A heat transfer rate control member (10) can be provided for controlling the rate of heat transfer between the reforming reaction section (6) and the feed gas passage (3). Thus, the rate of heat exchange between the reforming reaction section (6) and the fuel gas in the feed gas passage (3) can be properly controlled by the heat transfer rate control member (10), and the control over the rate of heat exchange can reduce temperature variations in the reforming reaction section (6).
In this case, the heat transfer rate control member (10) may be of fire-resistant thermal insulant. This easily provides a specific structure of the heat transfer rate control member (10).
The feed gas passage (3) may be provided in the vicinity of a reformed gas passage (11) communicating with an outlet (6b) of the reforming reaction section (6), and a heat exchanger (14) may be provided for exchanging heat between the feed gas in the feed gas passage (3) and the reformed gas in the reformed gas passage (11). Also in this case, the heat exchanger (14) is integrally formed as a preheater for preheating the feed gas between the feed gas passage (3) and the reformed gas passage (11), thereby making the construction of the reformer simple and compact.
The heat exchanger (14) preferably includes heat transfer fins (15), (16) that are presented to the feed gas passage (3) and the reformed gas passage (11), respectively, and extend along respective gas flows in the feed and reformed gas passages. Thus, gas pressure loss in the heat exchanger (14) can be reduced and the heat exchanger (14) can be compacted.
Further, the heat exchanger (14) may include porous materials (24), (25) (such as metallic foamed materials or ceramics foams) located in the feed gas passage (3) and the reformed gas passage (11), respectively. With this structure, heat exchange can be made by heat radiation through the porous materials (24), (25). This easily provides a specific structure of the heat exchanger (14).
Furthermore, the reforming reaction section (6), the feed gas passage (3), the reformed gas passage (11) and the heat transfer rate control member (10) may be provided integrally in a housing (1). Thus, the construction of the reformer can be further simplified, resulting in cost reduction.
The reforming reaction section (6) may be formed of a monolith (7) with a honeycomb structure. This provides the reforming reaction section (6) with a desirable structure.
The feed gas passage (3) may include a mixer for mixing components of the feed gas. In this case, the components of the feed gas are mixed by the mixer so that partial oxidation reaction can be efficiently effected in the reforming reaction section (6).
The heat exchanger (14) is preferably a parallel flow heat exchanger in which the feed gas in the feed gas passage (3) and the reformed gas in the reformed gas passage (11) flow in the same direction from inlet to outlet.
With this arrangement, even if the gas flow rate changes in the reforming reaction section (6) due to a load variation, the gas temperatures at the inlet and outlet of the reforming reaction section (6) can be each held substantially at a constant value without being affected by the change in gas flow rate. That is to say, since the amount of heat exchange in the heat exchanger (14) is constant, for a heat exchanger of the type which causes the feed gas and the reformed gas to flow in opposite directions from inlet to outlet, the heat exchange rate becomes excessive on reduction in gas flow rate so that the feed gas temperature at the inlet may rise excessively while the reformed gas temperature at the outlet may drop excessively. In contrast, for the parallel flow heat exchanger (14), there never arise such a problem.
The heat transfer fins (15), (16) may be bent in a corrugated shape. In this case, the heat transfer fins (15), (16), that is, the heat exchanger (14), can be easily manufactured.
The heat transfer fins (15), (16) may be fixed to surrounding walls by brazing. With this arrangement, the contact thermal resistance of the heat transfer fins (15), (16) to the surrounding walls is reduced thereby ensuring stable heat exchange performance with volume production.
The heat transfer fins (15), (16) may be each formed with slits (17). In this case, even if the gas passages (3), (11) are each divided into two sub-passages located at a heat transfer surface side thereof and its opposite side by the heat transfer fins (15), (16) in the heat exchanger (14), gases in both the sub-passages are mixed through the slits (17). This enables sufficient heat exchange of the gas in the opposite side sub-passage and provides high heat transfer performance at corners of the slit (17). Accordingly, heat exchange characteristics of the heat exchanger (14) can be improved.
The feed gas passage (3) may be provided at a portion thereof upstream from the heat exchanger (14) with a heat recovery section (34) formed of a substantially annular space which is located away from the reforming reaction section (6) or the heat exchanger (14) to surround at least one of the reforming reaction section (6) and the heat exchanger (14).
With this arrangement, heat dissipating from the reforming reaction section (6) to the surroundings can be recovered by the heat recovery section (34) to heat the feed gas. As a result, the heat loss of the entire partial oxidation reformer can be reduced so that the feed gas temperature at the inlet (6a) of the reforming reaction section (6) can be held at a temperature at which excellent catalytic reaction can be maintained in the reforming reaction section (6).
A heat transfer rate control member (22) may be interposed between the heat recovery section (34) and the reforming reaction section (6) or the heat exchanger (14). With this arrangement, the distance between the heat recovery section (34) and the reforming reaction section (6) or the heat exchanger (14) can be decreased thereby enabling compaction of the partial oxidation reformer with the provision of the heat recovery section (34).
Further, the heat recovery section (34) and the heat exchanger (14) may be communicated with each other through a single or plurality of communication passages (32). This simplifies the construction of the partial oxidation reformer and facilitates insertion of the heat transfer rate control member (22) to be interposed between the heat recovery section (34) and the reforming reaction section (6) or the heat exchanger (14), thereby facilitating fabrication of the partial oxidation reformer.
The reformed gas passage (11) may be provided in the vicinity of the reforming reaction section (6) to communicate the outlet (6b) of the reforming reaction section (6) with the heat exchanger (14) therethrough.
With this arrangement, the periphery of the reforming reaction section (6) is covered with the reformed gas passage (11) so as to be thermally insulated. Accordingly, the temperature in the reforming reaction section (6) can be held at catalytic reaction temperatures.
In addition, since the reformed gas passage (11) leading from the outlet (6b) of the reforming reaction section (6) to the heat exchanger (14) is integrally formed around the reformed reaction section (6) in the above manner, this makes the construction of the reformer simple and compact.
Further, the reforming reaction section (6) may be divided into a first reaction section (43) and a second reaction section (44), the second reaction section (44) being provided in the vicinity of the first reaction section (43) to communicate at an inlet thereof with an outlet of the first reaction section (43), and the first and second reaction sections (43), (44) may have gas flows in opposite directions.
Also in this case, the periphery of the first reaction section (43) of the reforming reaction section (6) is covered with the second reaction section (44) so as to be thermally insulated. Accordingly, the temperature in the reforming reaction section (6) can be maintained. In addition, since the reforming reaction section (6) itself has a double-wall structure, the reformer can have a simple and compact construction.
In each of the above arrangements, a heating means (20) may be provided for heating the feed gas at start-up. With this arrangement, the feed gas can be preheated exclusively at the start-up of the reformer, thereby reducing the start-up time of the reformer.